Major Fetal Hazards in Multiple Pregnancy

Abstract

Fetal risk in twin pregnancy is recognized as being about 2 to 4 times higher than in singletons. The main factors of this increased mortality are reviewed. Pathological effects associated with MZ origin are mainly due to the “third circulation” occurring in monochorial twins. Three situations can be distinguished: (a) hemodynamic equilibrium resulting in fetal growth impairment, (b) strong hemodynamic imbalance inducing fetal death, (c) moderate imbalance as the cause of “intertwin transfusion syndrome”. The acardiac and to some extent the papyraceus fetus can be considered as particular cases of the same problem. Other risks associated with MZ twins are the higher rate of malformations and umbilical cord entanglement in monoamniotic twins. The conjoined effects of prematurity and intrauterine growth retardation are undoubtedly the main cause of fetal death in multiple births. Therefore, some consideration is given to the underlying physiopathogenic factors. Prevention of twin weight defects demands early diagnosis of multiple pregnancy. As little can be expected from classical clinical methods, the obstetrician has to rely on more sophisticated techniques such as fetal ultrasonography. Even with an early diagnosis, at the present time there is no satisfactory treatment capable of preventing prematurity and retarded fetal growth. In this specific context, bed rest would appear as a fallacy.